1. Field of the Invention
The present invention relates to a method for producing an opto-electronic device array.
2. Description of the Related Art
In these days, large-scale integrated circuits (LSIs) are remarkably getting higher working speed due to improved performance of electronic devices such as bipolar transistors or field effect transistors. Compared with LSIs, printed-circuit boards, on which LSIs are mounted, generally have a lower working speed and even less so for racks including a plurality of such printed-circuit boards. This is resulted from differences of the respective basic clocks thereof. In a case of relatively long wiring, the basic clock is necessary to be suppressed so as to prevent transmission loss, noise influence and electromagnetic failure because the long wiring is susceptible thereto. Therefore, even if working speed of the LSIs is increased, performance of a system of the LSIs cannot be improved as much as expected. Wiring arts, in other words, packaging arts, are getting of greater importance compared with an art of improving the LSIs' working speed.
In view of the above problem concerning with the wiring arts, there are proposed some optical wiring devices for wiring among plural LSIs. Optical wiring devices are characterized by hardly having frequency dependency in transmission loss ranging from direct current (DC) up to several tens of giga-hertz (GHz). The optical wiring devices can easily achieve a transfer rate up to several tens Gbps because of not having electromagnetic failure and noise influence caused by earth potential change. The optical wiring devices are expected to provide high-speed transmission for interconnection between LSIs, therefore research and development is urgently progressed. To realize such optical wiring devices, an opto-electronic device array is required, in which several tens or hundreds of opto-electronic devices are disposed in even pitches so as to establish corresponding numbers of optical links.
However, the optical wiring devices have a problem of a production cost compared with conventional electrical wiring. The main reason is that the optical wiring devices are made of compound semiconductors such as GaAs or InP, which have higher material cost and higher production cost than Si. Si has an advantage in cost, however, light emitting devices of Si have extremely low light emission efficiency because Si is an indirect gap semiconductor. Especially, in a field of high-speed light emitting devices, there are no practical devices other than compound semiconductors. In this stage, there are no alternatives than applying compound semiconductors to such light emitting devices. Cost reduction is necessary to put the optical wiring arts into practical use.
An approach to reduce the cost for production of the opto-electronic device array is to improve efficiency of utilizing material thereof. For example, a semiconductor laser for compact discs (CD) has a device area of 300 μm×300 μm, however, an area no more than 10 μm×300 μm is employed as an active region for laser emission and rest of the device area is utilized for handling of the device and aid of heat radiation. In this example, provided that the rest were omitted, thirty devices could be formed in the area of 300 μm×300 μm in theory. In a case of vertical cavity surface emitting laser-diodes (VCSEL hereinafter), which become in practical use in recent years, each of active regions thereof has an area of about 10 μm×10 μm, therefore nine hundreds devices could be formed in the area of 300 μm×300 μm in theory.
Even though the theoretical consideration is extreme, current arts of production of opto-electronic devices made from compound semiconductors leave much to improve in view of efficiency of utilizing material. An approach to improve the efficiency is an art of so-called epitaxial lift-off (ELO hereinafter). A related art is disclosed in IEEE Journal on Selected Topics in Quantum Electronics Vol. 6, No. 6, p. 1231–1239. According to the epitaxial lift-off arts, a semiconductor structure is formed on a first substrate and transferred therefrom to a second substrate. Thereby the semiconductor structure can be employed on the second substrate.